1. Field of the Invention
The present invention relates generally to radar detection of targets, and more particularly to improvement in the "pulse compression" characteristics of optimum matched illumination-reception (OMIR) radar waveforms. The invention also addresses the more general problem of providing a mechanism for "gradually" switching between strictly OMIR radar waveforms and radar waveforms other than OMIR radar waveforms.
2. Description of the Related Art
It has previously been proposed to maximize the signal-to-noise ratio in OMIR waveforms by generating solutions to an eigensystem equation associated with the expected autocorrelation function for an impulse response of a target, and by subsequently choosing the solution which maximizes the echo energy while satisfying other system constraints. The autocorrelation function is obtained using a computer-aided design system model of the target, based upon known geometrical data and applying appropriate radar cross-section codes incorporating such parameters as additional scattering characteristics, bandwidth limitations, expected aspect angle variation, and inhomogeneous radar-absorbing codings. This type of system is described in U.S. patent application Ser. No. 643,140, filed Jan. 17, 1991, and in U.S. patent application Ser. No. 717,058, filed Jun. 18, 1991.
The waveforms s(t) generated by the above system have the form ##EQU3## where
.mu. is an eigenvalue of the integral equation,
.tau. is a dummy variable of integration representing the time over which s(t) interacts with the target,
T is the arbitrary duration of the transmitted pulse,
.gamma.(t,.tau.) is the kernel of the autocorrelation function and is given by ##EQU4##
h.sub.1 (t) is the impulse response of the target, and
T.sub.i .fwdarw.T.sub.f is an arbitrary observation interval.
Despite the obvious advantages of this previously disclosed OMIR radar system, however, its practicality is limited because the "pulse compression" of the resulting OMIR radar waveforms was not accounted for in the initial set of boundary value conditions used to define the problem addressed by the system. Poor pulse compression results in poor range resolution and/or poor temporal side lobe levels, which all but precludes their application to radar detection scenarios in which either significant clutter is present, or in which greater range resolution is required.